C40.20
BillableMalignant neoplasm of long bones of unspecified lower limb
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C40.20 an HCC code?
Yes. C40.20 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for C40.20
For C40.20to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C40.20 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C40.20 is the ICD-10-CM diagnosis code for malignant neoplasm of long bones of unspecified lower limb. Cancer that starts in the long bones of the leg when the specific side (right or left) is not documented or specified. C40.20 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of bone and articular cartilage (c40-c41).
Under the CMS-HCC V28 risk adjustment model, C40.20 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors (HCC 21) with a community, non-dual, aged base RAF weight of 0.545. Under the older CMS-HCC V24 model, C40.20 maps to Lymphoma and Other Cancers (HCC 10) with a community, non-dual, aged base RAF weight of 0.675. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
This unspecified code should be used only when laterality is truly undetermined; query provider if possible for side specification. Because C40.20 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for C40.20 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This unspecified code should be used only when laterality is truly undetermined; query provider if possible for side specification
- •Long bones of lower limb include femur, tibia, and fibula
Clinical Significance
Primary malignant neoplasm of the long bones (femur, tibia, fibula) of an unspecified lower limb. Osteosarcoma and Ewing sarcoma most commonly affect the long bones of the leg, particularly the distal femur and proximal tibia. Unspecified laterality should trigger a provider query as it reduces documentation quality.
Documentation Requirements
- ✓Attempt to clarify laterality through provider query or record review
- ✓Specific long bone involved (femur, tibia, or fibula)
- ✓Histologic type from biopsy (osteosarcoma, Ewing sarcoma, chondrosarcoma)
- ✓Primary vs. metastatic origin confirmed
- ✓Tumor staging and grade
- ✓Reason laterality is not specified
Commonly Confused Codes
- •C40.21 — Long bones of RIGHT lower limb; use when right is documented
- •C40.22 — Long bones of LEFT lower limb; use when left is documented
- •C40.30 — Short bones of unspecified lower limb; different anatomic axis (tarsal/metatarsal vs. femur/tibia/fibula)
- •C79.51 — Secondary malignant neoplasm of bone; for metastatic bone disease from lung, breast, or prostate primaries